This invention relates to drive mechanisms and more particularly, it concerns an improved drive mechanism for alternately driving one or the other of two rotatable spindles in opposite directions incident to feeding a tape or film strip between supply and take up spools.
The passage of a tape or film strip in opposite directions between a pair of spools to which opposite ends of the strip are fixed has traditionally involved the connection of a reversible motor alternately to the particular one of the two spools on which the strip is being wound while the other spool is allowed to rotate and unwind under the tension in the strip. Although such reversible motor drive systems are acceptable when the motor is deployed primarily to wind the strip on one or the other of the two spools, problems arise in this approach to film strip winding and rewinding where the motor is used also as a source of drive torque for other operating components.
In the motion picture viewing art, for example, viewing devices have been developed by which a film strip connected at opposite ends to supply and take-up spools supported within a film cassette is, after exposure, processed or developed, projected and rewound automatically in accordance with information supplied by the processed or unprocessed state of the cassette contained film strip. Exemplary disclosures of such systems are found in U.S. Pat. Nos. 3,771,862 issued Nov. 13, 1973 to Edwin H. Land and 3,941,465 issued Mar. 2, 1976 to Irwin E. Figge et al. In such viewer systems, the processed or unprocessed state of the cassette is detected electrically and used to position or index a programming cam system by which the apparatus will be operated automatically in either "project," "process," "rewind" or "off" modes of operation. Such systems must necessarily incorporate numerous driven components in addition to the cassette contained supply and take-up spools between which the film strip must be wound and unwound as during the project and rewind operations. Such additional driven components will include an incremental film feeding shuttle, an optical shutter, a cooling fan as well as indexing movement of the cam system by which the overall apparatus is programmed to the several modes of operation. Also, it is to be noted that with the exception of the direction of film strip travel, all such additional components are desirably driven in one direction only.
While such viewer systems in the past have required more than one electric motor, it is desirable from the standpoint of both economy and synchronous operation of system components, to employ only one electric motor for all components. Because the direction of film strip supply and take-up spool rotation is the only reversible component, it is also advantageous to arrange such a single drive motor to rotate in one direction only.